When manufacturing wood chips or flakes for further industrial applications, the wear on the edges of the cutting, respectively, flaking knives is so great that their service life commonly only encompasses a few hours. This results in approximately one thousand knife exchanges within one year. Since with increasing dullness of the cutting edges the quality of the manufactured wood chips, respectively, flakes is quickly reduced and, simultaneously, the amount of drive energy for the flaking machine increases substantially, it is unavoidable to exchange the dull knives within relatively short periods of time with sharpened knives.
This knife exchange for rotatably supported knife ring within the flaking machine is in general possible by providing a respective opening within the machine housing; however, in order to reduce the downtime it is common to first remove the knife ring as a whole and replace it with a second knife ring with sharpened knives. The actual knife exchange is then performed at the removed knife ring.
After reinserting the sharpened knives in the knife ring, the cutting edges of the knives must be positioned such that they protrude relative to the cylindrical inner wall surface of the knife ring formed by so-called wearing plates to an extent that corresponds to the desired thickness of the flakes or cuttings produced. For this purpose, a knife holder is required which allows the adjustment of the knife edges with a special adjustment means outside of the cutting machine. Accordingly, each individual knife of the prior art is connected in a releasable manner to a knife support plate which is provided with a reference surface indicating the respective position of the knife edge for the required protrusion corresponding to the cutting or flaking depth, whereby this reference surface comes into contact with a corresponding reference surface provided at the knife holder of the knife ring when the knife unit comprised of the knife and its knife support plate is fastened to the knife holder. In this manner, a reproducible cutting edge positioning with respect to the initial state of the cylindrical inner wall surface of the knife ring is ensured; however, the wear of the inner wall surfaces at certain locations is not taken into consideration. Over an extended period of time, especially when the wear of the inner wall surfaces is great, a constant increase of the thickness of the flakes, respectively, cuttings will result which is finally no longer acceptable with respect to given quality standards.
During the frequent knife exchanges the handling of the relatively heavy knife rings is cumbersome, and bears the danger of causing injuries. Furthermore, it is time consuming, especially because the knives, before the sharpening step, must be released from the knife support plates and afterwards must again be connected thereto whereby their edges must be adjusted to the theoretical protrusion value relative to the provided reference surfaces at the knife support plates.
There have been numerous suggestions to find ways to avoid the cumbersome handling of the knife ring, however, the solutions that have been known so far concern only those exchange methods in which the knife ring remains positioned in the flaking machine. Accordingly, these methods are only suitable for knife rings that are rotatably supported and are not applicable to stationary knife rings.
Such a method for exchanging the flaking knives in the knife ring which is mounted in the flaking machine is described in the British patent application GB 2 013 135 A. The knives may be exchanged after being released from their respective knife holder, however, a complicated adjusting device is required which allows the adjustment of the projection of the cutting edges of the flaking knives relative to the adjacent wall portions corresponding to the desired flake thickness directly on the knife ring. This adjusting device requires at least three cylinder/piston units. After shutting down the flaking machine, a first unit must be attached to the arrested rotor and the two other units must be fastened to the exterior of the machine housing in the area of a closeable opening. In addition to the constructive expenditure, the mounting and demounting of the adjusting device requires a considerable preparation time which in addition to the time-consuming actual knife exchange results in an economically unfeasible downtime. This exchange method therefore has not been successful in practice.
A different approach has been suggested with the German Patent DE 33 09 517 C1 which discloses a method for providing a continuous sharpness of the knives in which the downtime resulting from the knife exchange is prevented by providing strip steel knives which during the operation of the flaking machine are continuously or stepwise fed into the working zone of the machine depending on the respective wear condition. This method is limited to resharpening so-called disposable knives made of strip steel, and the exchange of high-quality knives that need to be repeatedly sharpened, the subject matter of the present invention, is expressly avoided.
It is therefore an object of the present invention to eliminate the cumbersome and time-consuming handling of the heavy knife rings during removal and remounting, as well as during adjustment of the cutting edges without causing a reduction in quality of the manufactured wood flakes. Also, while employing the known knife holders, an automatic knife exchange should be possible with the aid of spring forces. Furthermore, according to the present invention, the suggested method should also be compatible with conventional knife rings, if necessary, after minimal retro-fitting.